But for me - no. I have to face up to the fact I’ve ruined my life if I am ever going to claw back some of it.
Well, do you really have to claw it back? That sounds really punishing and not very realistic. It's OK to regret the past but the past is done and it can't/wont be clawed back. Some things really can't be repaired and then people really do have to build the best life they can out of the pieces. So maybe the best you can do is to accept that this is where you are now (bad though it may be) and to see where else you could move on to from here. If you recognise that you made bad choices in the past then you have learned something from 20 years of experience and you can make some better choices now. That may not be much comfort (and it doesn't guarantee that your choices from now on will be perfect either) but it's as good as it gets.
Maybe the best you can do is just to keep on keeping on. Change is an inbuilt part of life so even if you do nothing deliberately yourself, some of those changes that just happen may bring good things to you. "Keeping on keeping on" is very simple advice but it can also be very difficult to do. It can take a lot of effort. Which means that if you can do it then you do have something to feel proud of, instead of only being angry at yourself.
Getting through the day to day but with so much anger at yourself does sound (from the outside) very like moderate depression. Depression doesn't always feel like depression. Cheerful day to day, afraid to think of the future, and very angry with yourself for your past choices. That's very like functioning depression. And how are you not normal? You sound normal (if depressed) so far, but of course you have not shared any details. Being abnormal can make life hard. And surely being abnormal is a mitigating factor in some of the poor choices you have made?
I have no idea if any of that''s helpful, I suspect it isn't. Feel free to ignore. 